Publicação
Nesting habitat preferences and nest predation of green turtles (Chelonia mydas) in the Bijagós Archipelago, Guinea Bissau
| Resumo: | The nesting process requires sea turtles to choose among beach habitats that ensure a successful development of eggs and a low risk of mortality due to predation. The nesting habitat preferences of green turtles (Chelonia mydas) in João Vieira Island were analysed, as well as the proportion of emergences resulting in a successful nesting event and the effects of lunar and tidal phases on the nesting behaviour. The susceptibility of nests to predation at the different habitats were also analysed and nest predation rates were compared with the ones of Poilão Island. Of the habitat features evaluated (offshore bathymetry, slope, distance from highest spring tide line to forest, cliff height, vegetation height, ghost crabs burrows, and sand characteristics i.e. colour, grain size, pH and albedo), beach slope and vegetation height appeared to have the greatest influence on the emergence decision. Nevertheless, the distribution of successful nesting attempts revealed that green turtles showed a strong preference to nest on supra-littoral low height herbaceous vegetation areas. In addition, many unsuccessful nesting attempts were observed on shrubland. Green turtles nests on João Vieira experienced a severe predation (76%) by monitor lizards (Varanus niloticus) during the first 10 days after oviposition. No evidence of predation, or of predation attempts was found on Poilão. These differences between islands suggest that the extremely high nest density occurring in Poilão may reduce per-nest predation rates due to predator satiation. This study has made important findings on the habitat preferences of green turtles nesting in João Vieira, and provided basic ecological information about the nesting process and on the nest predation risks. The results also allow to better informing on the need of adequate monitoring and protection strategies. |
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| Autores principais: | Ferreira, Maria Betânia Martins da Silva, 1979- |
| Assunto: | Herpetologia Nidificação Predação Tartarugas marinhas Guiné-Bissau Teses de mestrado - 2012 |
| Ano: | 2012 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | The nesting process requires sea turtles to choose among beach habitats that ensure a successful development of eggs and a low risk of mortality due to predation. The nesting habitat preferences of green turtles (Chelonia mydas) in João Vieira Island were analysed, as well as the proportion of emergences resulting in a successful nesting event and the effects of lunar and tidal phases on the nesting behaviour. The susceptibility of nests to predation at the different habitats were also analysed and nest predation rates were compared with the ones of Poilão Island. Of the habitat features evaluated (offshore bathymetry, slope, distance from highest spring tide line to forest, cliff height, vegetation height, ghost crabs burrows, and sand characteristics i.e. colour, grain size, pH and albedo), beach slope and vegetation height appeared to have the greatest influence on the emergence decision. Nevertheless, the distribution of successful nesting attempts revealed that green turtles showed a strong preference to nest on supra-littoral low height herbaceous vegetation areas. In addition, many unsuccessful nesting attempts were observed on shrubland. Green turtles nests on João Vieira experienced a severe predation (76%) by monitor lizards (Varanus niloticus) during the first 10 days after oviposition. No evidence of predation, or of predation attempts was found on Poilão. These differences between islands suggest that the extremely high nest density occurring in Poilão may reduce per-nest predation rates due to predator satiation. This study has made important findings on the habitat preferences of green turtles nesting in João Vieira, and provided basic ecological information about the nesting process and on the nest predation risks. The results also allow to better informing on the need of adequate monitoring and protection strategies. |
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